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					| Cretaceous-Tertiary Extinctions |  
					| Lecture 25 5/11/98
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					| |  | The Cretaceous-Tertiary extinctions resulted in the extinction of the dinosaurs and many other groups. As a result it opened environments and paved the way for modern floras and faunas. | 
 |  | The Cretaceous-Tertiary extinctions are one of the major extinction events in the history of life | 
 |  | Unlike the Permian-Triassic extinctions, the Cretaceous-Tertiary extinctions appear to be sudden. | 
 |  | An asteroid impact at the time appears to have played a major role in the extinction. | 
 |  | 15% of all marine families | 
 |  | 50 % at generic level, maybe 80-90 % of all species | 
 |  | concentrated on planton, marine predators, and shallow water communities | 
 |  | 25 % of terrestrial families | 
 |  | nothing bigger than 25 kg survived | 
 |  | Appears to be very sudden | 
 |  | The Cretaceous-Tertiary boundary sediments | 
 |  | well described around the world | 
 |  | can be shown to be a single bed | 
 |  | A wide range of suggested | 
 |  | climatic change to dinosaur blindness | 
 |  | several events took place at or near the boundary | 
 |  | Discovery of irridium in boundary clay | 
 |  | Similary deposits were found world wide | 
 |  | Other materials in the boundary layer | 
 |  | Irridium is rare on the surface of the earth | 
 |  | Irridium is much more common in space | 
 |  | Discovery of an Impact Crater | 
 |  | Chicxulub Impact structure | 
 |  | Buried beneath the Yucatan Peninsula | 
 |  | Age dates of melt rock in the structure have at date of 65 Ma | 
 | Did the Impact cause the extinctions? | 
 |  | This remains an issue of contention | 
 |  | You must explain all of the extinctions | 
 |  | We don't understand all of the implications the event | 
 |  | Impact wipes out most plankton & primary production | 
 |  | This lose travels up the food chain and heavily impacts top order consumers | 
 |  | Smaller organisms may survive by burrowing, hibernating, or migrating | 
 |  | Shallow marine faunas hit by acid rains and temperature changes | 
 |  | Plants & planton return from resting spores & seeds to repopulate planet. | 
 
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